Lafferty and Pk'J'hybridgh — On a Phytophthora Parasitic on Ai^fles. 37 



two types already described ; and in all cases those with amphi,gynons antheridia 

 were veiy nineh rarer tlian those in which the antheridia were paragynous. 

 Illustrations of both types of these organs for the Phytophthoras under considera- 

 tion are provided in PL I, figs. 1-14, and PI. II, figs. 1-12. 



Further, in all cases except P. Syringae and the Irish fungus, a second form 

 of asexual reproductive body was found in varying abundance, which had not 

 hitherto been described for P. Cadorum or P. Fagi. With regard to the latter 

 fungus, these bodies were not found in cultures on sterilised media, but only on 

 cultures on living apples. 



These bodies, which may provisionally be called sphacro-conidia, are usually 

 intercalary in origin, althougli they may sometimes be terminal. The hyphae on 

 which they are borne are generally somewhat stouter than those which bear 

 sporangia. They are, as a rule, uniformly spherical in shape ; but, in rare 

 instances, tliey develop a papilla resembling that found in a sporangium. Their 

 thin walls give the same micro-chemical reactions as those given by the sporangial 

 walls. In diameter they vary from ooju to 40fj, and there is a tendency for them 

 to be slightly larger when produced on living apple than on sterilised media, such 

 as Quaker Oat agar, &c. Not infrequently short, slender hyplial outgrowths 

 proceed from them, which, however, must not be confounded with germ tubes. 

 Illustrations of sphaero-conidia are reproduced in fig. 13, PL II.. 



In hanging drops of water these sphaero-conidia have been found to produce 

 germ tubes, which may arise at any point on their surfaces. After growing a 

 short distance a germ tube may cease to grow, or may give rise to a terminal 

 second sphaero-conidium or to a normal sporangium. It is possible that the 

 sphaero-conidia possessing papillae may germinate by means of zoospores ; but up 

 to the present only the germination of the much more abundant non-papillate 

 forms has been observed. 



" Besting " conidia and chlamydospores have been described as occurring in 

 Plilltophthora Arccae (Golem.), P. Colocasiae But. & KuL, P. Faheri MaubL, 

 P. jatro-phae, Jens., P. Meaclii M'Kae, P. Nicotianae de H., P. jxirasitica Dast., 

 P. terrestria Sherb., and P. Theobromac Golem. In some cases they are thick- 

 walled, and are perhaps true chlamydospores, or possibly parthenogenetic oospores. 

 In others the walls are not so thick, and germiiiation is sometimes by zoospores. 

 The relation of these bodies to one another and to tliose described here for 

 P. Cadorum and P. Fagi require further investigation. 



The sporangia of the English, American, and Swiss Phytophthoras, as well as 

 those of P. Cadorum and /'. Fagi, resembled one another in being always papillate, 

 the papilla being, in reality, a hyaline thickening of the sporangial wall, and 

 forming a distinct projection or protuberance. (See PI. I, fig. 16, and PL II, 

 figs. 14 and 15.) In the Irish fungus and in P. Syringas, on the other hand, 

 although the wall at the distal end of the sporangium is thickened and hyaline, 

 yet there is no distinct papilla, the end being flattened or rounded. 



There was considerable variation in the size of the sporangia. In the case of 

 the four first-mentioned fungi they averaged 37/^ x 27m on artificial media, such 

 as Quaker oat agar, &c. ; but they were considerably larger, viz. 52/x x 30/u, on raw 

 apple tissue. In the case of P. Fagi they averaged 45,i( x 31ju on artificial media 

 and 56^ x yl^ on raw apple tissue In P. Syringae and in the Irish fungus they 

 measured 38/.t x 26/i and 40/^ x 27,u respectively on artificial media, but they 

 were not abundant enougli on raw apple tissue to permit average measurements 

 being made. 



Too much stress, of course, must not be laid on the sizes of sporangia as a 



